Remote control system



Oct. 16, 1945. A. L. JEROME ET AL 2,387,152

' REMOTE CONTROL SYSTEM Filed Feb. 2, 1944 s Sheets-Shet '1 I if] ll can 17 i,1 m [H [WV/z- JWZ Y i Ofifiiee 6M 125 1 E] i F 1 i 55 131i; 75 0; Egg/ B 124 I 1 l4 v i v V VINVENTORJ. Ari/zap L. Jerome and BY Lloyd Vlewc'jr mam THEIR ATTORNEY Oct. 16, 1945. A. 1.; JEROME ET AL 2,387,152

REMOTE QONTROL SYSTEM Filed Feb. 2, 1944 3 SheetsSheet 2 TL U lmpiim. H .0 5. 5m WA l w. m lilnlu. W u. M M 1 W MV 5? 9/. .1 a l. T R W Fm W 4 I o 5 A 5. 6 W0 3 I T m B 0 A 7 WM A1 M r 0 6 5 51 w n 5 A Z .1 B w 6 0 S .05-- 1% M 0 M0 0 PFY 6 I M W M m w WW a 5 6 w m v w W M l y 5 .I. M 6 0 5 E R 6 5 9 T 5.--} E 7 H w H m y A Y T m Z P mm H r 4 w W 0 r 00 "+053 M" 6 55 INVEN'ILORS [[20 and A. L.-JEROME ET AL" 2,387,152

REMOTE CONTROL SYSTEM Filed Feb. 2, 1944 s Sheets-Sheet '3 W L 1i AP/fflll Z JZ P [loyal Vlewzm WZP ZHEIIL ATTORNEY m 7 n m v m L U m w aw? E V m M .v Mp? P m 62 I M 1 my v z k 0 Mm f t Z 1 a WW 0 n W. H w r5 F 29 ar 56 1 3 1 2: i

Oct. 16, 1 945.

Patented Oct. 16, 1945 REMOTE CONTROL SYSTEM Arthur L. Jerome, Edgewood, and Lloyd V. Lewis, Pittsburgh, Pa., assignors to The UnionSwitch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application February 2, 1944, Serial No. 520,718

40 Claims.

Our invention relates to a direct wire remote control and indication system, and particularly to means for controlling a railway track switch and the signals associated therewith from a distant point of control, such as a train dispatchers ofiice, andfor indicating at the office the conditively long distances in an economical manner,

and which possesses a high degree of immunity against anyinterference resulting from the joint use of the same line wires by other communication facilities, or from any foreign current interference likely to occur in long distance line circuits.

Another object of our invention is to provide a system of the type described which is arranged so as to be normally inactive and to become active whenever a control member is manually operated to transmit a switch or Signal control code.

A further object of the invention is to provide a system of the type described which is normally inactive and whichautomatically becomes active when a train entersan approach section leading to the switch governed by the control system.

Another object of the invention is to provide a system of the type described incorporating means for insuring that. after a signal controlled by this system is put to stop by a passing train, it will not be cleared again" except by the wil1 of the operator at the point of control.

A further object of the invention is to provide a system of the type described and incorporating means for preventing storage of switch control.

Another object of the invention is to provide a system of the type described which employs master code of '75, 120 and 180 code frequency for switch and signal control, and employs feedback energy of one polarity to indicate the position of the track switch and of the other polarity to indicate the condition ofthe signals.

A further object of the invention is to provide a system of the type described incorporating means to modify the feed-back energy of either polarity to provide an indication of occupancy of the approach section leading to the track switch. V

Another object/0f the'invention is to provide a system of the type described which is arranged so that when a signal control code'is beingtransmitted over the line circuit movement of the switch control lever is without efiect.

A further object of the invention is to provide a system of the type described which can be caused to assume an inactive condition when and only when continued operation of the system is not required.

Another object of our inventionis to provide a system of the type described which is so arranged that, after a signal has been cleared, it cannot be restored to stop by the operation of any lever other than its control lever. V 7

Another object of our invention is to provide a system of the type described which is arranged to become inactive when its continued operation is not required A further object of our invention is to provide an improved form of feed-back apparatus suitable for use in systems employing continuously transmitted impulse codes, which is so, arranged that it will not respond falsely in the presence of foreign current.

We shall describe one form of apparatus embodying our invention, together with a modification which we may employ, and shall then point out the novel features thereof in claims.

In the drawings: l

Figs. 1A and 1B taken together are a diagram of a remote .control system provided by this invention, and

Fig. 2 is a diagram of a modified formyof 'office I equipment which may be employed inplace of that shown in Fig. 1A.

Similar reference characters refer to similar parts in each of the several views.

In practicing our invention, we provide a lin channel between the office and the field station and provide means at the office controlled by a two-position switch control lever for supplying to the line channel master code energy of one polarity or another depending upon the position of the switch control lever, while the equipment at the field station is controlled in accordance with the polarity of the master code impulses to move the switch to its normal or reverse positions. When the switch corresponds in position to the polarity of the master code, feed-back energy of normal polarity is supplied to the line channel are constructed in the manner shown in Letters Patent of the United States No. 1,773,472 to Paul N. Bossart, except that the unit IZBDU is provided with an additional tuned circuit to render it more fully non-responsiye to energy of 180 code frequency than the usual unit of this type.

The operation of the resonant unit I20DU is such that sufficient energy is supplied through the unit to pick uprelay LHR when and only when the code following line relay controlling the supply of energy to the decoding transformer DT is operated by coded energy of 120 code frequency, while the unit I80DU operates so that sufficient energy is supplied through the unit to pick up relay RHR when and only when the code following line relay controlling the supply of energy to the decoding transformer DT is operated by coded energy of 180 code frequency.

The decoding transformer DT is provided with a secondary winding 96 from which energy is supplied to the impulse relay IR which controls the supply of impulses of feed-back energy to the line circuit connecting the office and field station. The relay IR is of a type the contacts of which pick up only when energy of a particular polarity is supplied to the relay, while the relay and the secondary winding of the decoding transformer are arranged so that energy of the polarity effective to pick up the contacts of the relay IR is supplied to the relay on release of the contacts of the coding relay governing the supply of energy to the decoding transformer.

The relay IR also controls the supply of energy to half-step relays TA and TB which operate at times, as hereafter explained, to cause an impulse of feed-back energy to be supplied to-the line wires only every other time the contacts of the impulse relay pick up instead of every time they pick up.

The code following line relays NCF and RCF also control the supply of energy to a decoding unit IDU from which energy is supplied to the pick-up winding of a stick repeater relay TS for the detector section track relay TR. The unit I5DU is arranged as shown in Letters Patent of the United States No. 2,218,124 to Andrew J. Sorensen, and includes a polarized relay PR having two windings which are alternately energized in series with the two portions of the primary winding of a transformer, while a contact of the relay PR rectifies the energy supplied from the secondary winding of this transformer to the pick-up winding of the rela TS. The relay PR is arranged so that energy supplied to one winding of the relay moves the relay contact to one position and energy supplied to the other winding of the relay moves the relay contact toits other position, while the transformer is arranged so 7 that energy supplied to one portion of the transformer primary winding creates flux of one polarity in the transformer core and energy supplied to the other portion of the transformer primary winding creates flux of the other polarity in the transformer core.

The relay PR and the associated transformer are proportioned so that when the code following relay governing the circuits of the relay and transformer is operated by energy of 75 code frequency the contact of relay PR will be moved between its two positions in response to alternate energization of the relay windings and will therefore rectify the energy supplied from the transformer secondary winding to relay TS. The relay PR and the associated transformer are also proportioned so that if the coding relay governing the circuits of the relay and transformer is operated by coded energy of a code frequency higher than 75 code frequency as, for example, energy of or code frequency, the contact of relay PR will not respond to alternate energization of the relay windings, but will remain in one position and consequently will not rectify the energy supplied from the secondary winding of the transformer to the relay TS. The relay TS is a direct current relay and will not respond to alternating current and when its contacts are released they will not be picked up by energy 'upplied from the transformer to the relay pick up winding unless this energy is rectified by the periodic operation of relay PR.

Referring now to Fig. 1A, the oifice equipment includes a miniature track diagram corresponding to the track plan of Fig. 1B, provided with a red lamp TK controlled by a track indication relay TKR for indicating the condition of occupancy of the detector section T, and a red lamp AK controlled by an approach indication relay AKR for indicating the condition of occupancy of the approach section AT.

To effect the manual control of the switch and signals, a switch control lever WL having a normal and a reverse position, and a signal control lever SGL having a normal position and righthand. and left-hand signal clearing positions are provided, as shown. These levers are preferably of the push-turn type, such as is shown in Letters Patent of the United States No. 2,289,736, to C. S. Snavely and R. H. Zetwo, and are mounted on a suitable control panel below the track diagram.

It is to be understood that the rotatable contacts 83, I6, etc. of each such lever are locked in their different control positions by a spring actuated detent which also serves to close an auxiliary contact such as contact 15, and that the lever handle must be pressed to move the shaft axially so as to open the auxiliary contact in order to release the detent and to rotate the control contacts from one position to another.'

Associated with the switch control lever WL is a lever repeating relay WLP of the stick polar type, a slow pick-up correspondence relay COR, a slow release indication relay KR, and two yellow indication lamps NWK and RWK for indicat-. ing the normal and reverse positions, respectively, of the track switch controlled by lever WL. Associated with the signal control lever SGL is a stick storage relay HS, controlled by the lever in either of its reverse positions and also by relay KR, a red indication lamp NHK for indicating that the signals controlled by lever SGL are at stop, and two green indication lamps LHK and RHK for indicating that a signal controlled by lever SGL for'go-verning traffic movements to the left or right, respectively, has been cleared. The ofiice equipment also includes a set of three code transmitters 75CT, i20CT and IBiBCT, which when supplied with energy operate their contacts periodically at the rate of 75, 120 or 180 times per minute, respectively, to generate impulse codes of the corresponding frequencies. These code transmitters govern a coding relay CTM, which is operated periodically by one code transmitter or another to deliver the code of corresponding frequency to the line circuit.

When the coding relay CTM is released, its contacts It) and l I connect a code following feedback detector relay KS across the line wires Y and Z and, when relay CTM is energized, its

contacts l0 and H connect a line battery LB 'across theline wires YandZ. Relay KS is of a biased. polartypewhich respondsonly when positive current is supplied to the. left-hand terminal of: its winding, as indicated. by the arrow on the drawings.

Relay KS controls a slow release repeating relay'KF which jointly with relay KS controls the indication relay KR so that relay KR is held steadily picked up in response to the periodic operation of relay KS.

Relays KS and CTM jointly control an auxiliary detector relay KSA in such amanner that relay KSA is held. steadily picked up if relay KS operates each time relay CTM operates, and is operated periodically if relay KS operates only during alternate operations of relay CTM. Relay- KSA. controls a repeating relay KB: which jointlywith relay KSA causes the approach indication relay AKR to be held steadily picked up when relay KSA operates periodically.

The equipment of Fig. 1A includes also a push button PB and a stick relay PBR associated therewith, relay PBR serving as a cut-out relay by means of which the coding system may be restored manuallyto an inactive state :under predetermined conditions. The equipment of Fig. 2 includes an alternative arrangement employing a slow release relay ZR as a cut-out relay by means of which the equipment is restored automatically to its inactive condition under predetermined'conditions.

The ofiice and field station are each provided with a suitable source of direct current, such as a storage battery, not shown, the positive and negative terminals of which are designated 13' and C, respectively, in the drawings.

In most instances in the drawings, the relay contacts are shown directly in line with the winding of the relay; but in some instances, in order to simplify the drawings, relay contacts are shown separated from the relay winding, and where this is done the relay with whichthe contacts are associated is indicated by appropriate reference characters located above the contacts.

The equipment of Figs. 1A and 13, as shown, is in its normal inactive condition. The correspondence relay COR is energized over a circuit extending from one terminal B of the local source of current over the normally closed push contacts M'and I5 of levers SGL and WL, and thence over the rotatable contact l6 of lever WL and contact ll. of relay WLP in' corresponding normal or reverse positions, through relay COR to terminal C. Energy is supplied to push button stick relay PBR over its stick circuit which extends from terminal B at normally closed contact M of lever SGL over contact l8 of lever SGL in its normal center position, front contact 20' of relay TKR. front contact 2i of relay COR, back contact 23 of relay AKR, front contact 22, and the winding of relay PBR to terminal C.

The energy supplied to relay PBR keeps its contacts picked up so that its contact 24 interrupts the circuits of'the code transmitters 150T, I-ZilCT, and I8BCT and these. devices do not operate at this time. In addition, contact 25 of relay PBR establishes a circu t including back contact 21 of relay HS for supplying energy to coding relay CTM and its contacts are picked up so that the line battery LB is connected across the line wires Y and Z in series with the line Winding 29 of the indication relay TKR. I

As the contacts of relay WLP are in their normal positions the positive terminal of battery LB is connected: through winding 29 of relay TKR,

left-hand polar contact. 30' ofrelay WLP, and front contact 10 of relay to the line wire Y, while the negative terminal of the battery LB'is connected over left-hand polar contact 3| of relay WLP, and front contact H ofrelay CTM- toline wire Z. The current now supplied from battery LB to the line Wires may be considered to be of normal polarity and this current is transmitted over the line wires to the fieldstation where it flowsf-romwire Y over front contact 33 of the detector section track relay TR, front contact 34 of the approach section trackrelay AR, back. contact 35. of impulse relay IR, windings of relays NCF and RCF from left to right, and back contact36 of relay IE to line wire Z.

The energy supplied from the line battery LB through the line winding 29 of. relay 'I'KR. to the line wires keeps the contacts of relay TKR picked up so that its contact 20: maintains the circuit of relay PBR closed, and its contact 3.! interrupts the circuit of lamp TKJ At this time the relays at the oilice other than thosementioned are released, and, as relay KR isreleased, its contact 40 interrupts the circuits of the switch and signal indication lights and these lights are all extinguished, while contact 41 of relay AKR interrupts the circuit of lamp AK.

The energy nowsupplied over the line wires Y and Z to the linerelays- NCF and RCF being of normal polarity picks up relay NCF, but does not pick up relay RCF, which is responsive only. to line current of reverse polarity. As relay NCF is picked up, energy is supplied. over its front contact 42 to. relay NWR and its contactsare picked up. so that energy of normal polarity is supplied to the switch control relay WR over front contact 44 of relay NWR, front contact 45 of lock relay LR, winding of relay WR, front contact 46 of relay LR, and back contact 41 of relay RWR. The energy supplied to relay WR causes it to close its neutral front contacts and causes its polar contacts to assume the normal position so that the switch machine SM is controlled in such a man.- ner as to maintain the track switch SW locked mechaniaclly in its normal position, as shown. Suitable circuits forcontrolling the switch machine SM by relay WR and for controlling the switch indication relay WP are well known and since these are not part of our invention they have been shown diagrammatically in the draw- As relay NCF is steadily picked up its contact interrupts the circuit of relay CD and its contact 41 is consequently open, interrupting the circuit for the primary winding of decoding transformer DT, and the circuit for the decodingunit I5DU.

As the switch SW is in its normal position, energy of normal polarity is supplied to relay WP and relay NWP is. energized by current supp over front neutral contact 5!) and normal polar contact 5! of relay WP and normal polar contact 52 of relay WR.

At this time the approach locking relay LAS is energized by current supplied over its stick circuit which may be traced from terminal B at back contact 5| of signal relay LBH, over back contact 52 of signal relay LAH, back contact 53 of line relay LHDR, front contact 54, and the winding of relay LAS to terminal C. Accordingly, relay LAS is maintained picked up and its contact 55 prevents the supply of energy to signal relays LAH and LBH to thereby maintain the display of stop indications by signals LA and LB;

Similarly, the approach locking relay RAS is energized by current supplied over its stick circuit which may be traced from terminal B at back contact 58 of relay RBH, over back contact 59 of relay RAH, back contact 60 of relay RHDR, front contact 6|, and the winding of relay RAS to terminal C. The contacts of relay RAS, .therefore, are picked up and contact 62 prevents the supply of energy to signal relays RAH and RBH and these relays remain released to maintain the displayof stop indications by signals RA and RB.

As pointed out above, the equipment at the ofiice operates at this time to supply steady energy to the line wires and the line relay NCF is steadily picked up so energy is not supplied through the decoding transformer DT to the signal control relays LHR and RHR and their contacts are released. Accordingly, contacts 64 and 65 of relay LHR interrupt the circuit of signal line relay LHDR, while contacts 66 and 61 of relay RHR interrupt the circuit of signal line relay RHDR.

At this time the relay TS is energized by current supplied to its holding winding over the relay stick circuit which includes its own front contact 68 and front contact 69 of the detector section track relay TR. The switch locking relay LR is energized by current supplied over its stick circuit and over one of its pick-up circuits. Both of these circuits include front contact 10 of relay RAS, front contact H of relay LAS, front contact 12 of relay TR, and front contact 73 of relay TS, while the stick circuit for. relay LR includes its own front contact 14, and the pickup circuit which is established at this time includes normal polar contact 16 of relay WP and front contact 11 of relay NWR. The relay LR, therefore, is picked up and its contacts 45 and 46 establish the circuits controlled by relays NWR and RWR for supplying energy to the switch control relay WR, while contact 80 of relay LR interrupts the circuits for supplying energy to 1 the signal relays LAH, LBH, RAH and RBH and thereby insures that the signals all display stop indications.

This equipment is arranged so that when it is in its inactive condition, it is manually set into operation on movement of either the switch or the signal control lever, or automatically on occupancy of the approach or detector sections.

For purposes of illustration it will be assumed that the equipment is in its inactive condition as described in detail above, and that the operator at the office wishes to move the switch SW from its normal to its reverse position.

In order to cause this movement of the switch SW, the operator moves the switch control lever WL from its left-hand or normal position to its right-hand or reverse position. As stated above, the lever WL is of the push-turn type and before thelever can be turned it must be depressed with the result that contact l5 interrupts the circuit of the slow pick-up correspondence relay COR so that its contact 2| opens to interrupt the stick circuit of push button stick relay PBR. In addition, on release of relay COR its contact 8| interrupts the pick-up circuit of relay HS, while contact 82 of relay COR interrupts the circuits of the switch and signal indication lamps to pro-' vide a dark interval following each lever movement and to permit the indication relays to become stabilized before the lamp circuits are established.

0n movement of the lever WL to its righthand position, its contact 83 interrupts the circuit of the upper winding of relay WLP and establishes the circuit of the lower winding of the relay and thus causes the relay contacts to move to the right-hand or reverse position. When the contacts of relay WLP are in their reverse position and the lever contact [5 is closed, energy is again supplied to relay COR and after a short time interval, relay COR picks up. Relay PBR remains released and its contact 24 establishes circuits for the code transmitters I2BCT, IBDCT and 150T and these devices operate periodically at their respective rates. In addition, on release of relay PBR, its contact 25 interrupts the supply of steady energy to coding relay CTM and connects relay CTM to the contact of code transmitter HOT 50 that coding relay CTM operates periodically to supply energy of 75 code frequency from battery LB to the line wires Y and Z.

On movement of the contacts 30 and 3| of relay, WLP from their normal to their reverse position, the polarity of the current supplied from battery LB to the line wires Y and Z is changed from normal to reverse, the positive terminal of the battery being connected through winding 29 of relay TKR, reverse polar contact 30 of relay WLP, and front contact ll of relay CTM to line wire Z. During the release periods of relay CTM, the supply of energy through winding 29 of relay TKR is cut off, but at these times energy is supplied locally over back contact 85 of relay CTM and front contact 86 of relay TKR to th holding winding 81' of relay TKR. As relay TKR is energized in both the picked-up and released periods of relay CTM, the contacts of relay TKR remain picked up.

When the supply of energy .of normal polarity to the line wires Y and Z is out 01f, relay NCF at the field station releases and interrupts the circuit of relay NWR, which relay releases in turn to out 01f the supply of energy of normal polarity to switch control relay WR.

The energy of 75 code frequency and reverse polarity supplied over the line wires Y and Z to the field station causes code following operation of relay RCF with the result that energy is supplied over its front contact 89 to relay RWR, and is supplied over back contact 89, front contact 90 of relay RWR, and back contact 9| of relay NWR to relay CD. The relays RWR and CD are slow to release so their contacts remain picked up during the periods in which the supply of energy to the relay windings is interrupted.

When relay RWR picks up, energy of reverse polarity is supplied to the switch control relay WR over the circuit extending from terminal B at front contact 41 of relay RWR, over front contact 46 of relay LR, winding of relay WR, front contact '45 of relay LR, and back contact 44 of relay NWR to terminal C. This causes the polar contacts of relay WR to move to their. reverse positions so that contact 92 establishes the circuit to cause the switch machine SM to move the switch SW to its reverse position, while contact 52 of relay WR interrupts the circuit of relay NWP and it releases to prevent energization of the line relays LHDR and RI-IDR, and the signal relays LAH, LBH, RAH and RBH.

When the switch SW completesits movement to its reverse position, energy of reverse polarity is supplied to relay WP and its polar contacts shift to their reverse positions so that energy is supplied to'relay RWP over front contact 50 of relay 'WP, reverse polar contact 5| of relay WP,

ment to the normal position relay IR operates to supply impulses of feed-back energy'of normal polarity to the line wires to operate relay KS to pick up relay KB, and establish the circuits of the normal switch and signal indication lamps.

Operation of equipment to control the signals This system is arranged so that when feedback energy is received at the olfice to indicate that the position of the switch corresponds to the polarity of the coded energy transmitted from the office, the operator may clear the signals governing movement of trafiic in either direction over the switch.

The signal lever SGL may be moved following movement of the switch lever WL, or may be moved at a time when the relay PBR is picked up and the equipment is inactive. In either event, movement of the lever SGL is ineffective to cause signal control energy to be transmitted until a For example, this arrangement prevents improper supply of energy to relay HS and thus prevents improper transmission of a signal control code if the switch lever WL is moved and the switch indication is received, as explained above,

to pick up relay KR. The signal leverSGL is of the push-turn type and if it is moved at a time when relay PBR is picked up, contacts I4 and will maintain the switch in its existing position and will cause feed-back energy of normal polarity to be supplied over the line wires to operate relay KS to pick up relay KR.

When the signal lever SGL is moved to either its left-hand or right-hand position, its contact i8 interrupts the circuit for relay WLP, thereby rendering relay WLP non-responsive to the movement of the switch lever WL except when lever SGL is in its normal center position. This prevents a change in the polarity of the current supplied to the line While a signal control code is being transmitted and thereby insures that a cleared signal will not be disturbed as a result of the inadvertent movement of the switch control lever, and it also prevents a change in the position of the switch during the transmission of a signal control code,even though the signals remain at stop and the switch is free to respond.

If the switch control lever WL is moved when the signal control lever SGL is reversed, relay COR releases because lever WL and relay WLP are out of correspondence, thereby extinguishing the switch and signal indication lamps.

On movement of lever SGL, its contact I4 interrupts the circuit of relay COR and its contacts release, but as soon as pressure is removed from the lever, its contact l4 reestablishes the circuit of rela COR and its contacts pick up after a short time interval, assuming that the circuit of the relay is complete. When relay COR releases, its contact H5 interrupts the circuits of the relays KB and KR and the relay COR is slow enough in picking up to remain released until the relay KR releases. When relay COR picks up, its contact H5 reestablishes the circuit of relays KF and KR and as a result of continued code following operation of relay KS the relays KF and KR'pick up so that energy may be supplied tothe relay HS.

The arrangement just described insures that on movement of the signal lever SGL, the relay HS will not be picked up unless after the lever has been; moved conditions are proper for a signal controlcodeto be. ransmitted.

signal lever SGL is moved immediately thereafter, before relay KR releases.

When the signal lever SGL is in either its left or its right-hand position and relays COR and KR are picked up, energ is supplied to relay HS over the circuit including contacts l4 and I3 of lever SGL, front contact 8| of relay COR, and front contact I22 of relay KR, and when relay HS picks up, its contact I24 establishes a stick circuit to keep the relay picked up as long as the signal lever SGL remains in the reverse position, irrespective of the condition of relays COR and KR.

When relay HS picks up, its contacts 185 and I0! change the connection between winding of relay KS and the line wires Y and Z so that relay KS is no longer responsive to feed-back energy of normal polarity but is rendered responsive only to feed-back energy of reverse polarity. Accordingly, relay KS releases and then relays KB and KR release and relay KSA remains released. When relay KR releases, its contact I22 interrupts the pick-up circuit for relay HS, but relay HS is maintained picked up by energy supplied over its stick circuit.

In addition, when relay HS picks up, its contact l2! interrupts the circuit for lamp NHK and establishes the circuit controlled by signal lever contact E25 for supplyin energy to one or the other of the lamps LHK and RHK. The lamp circuits are controlled by contact 40 of relay KR but since relay KR is released, the lamp circuits are interrupted and the lamps LHK and RHK remain dark until relay KR picks up in response to the operation of relay KS with relay HS picked up.

When relay HS picks up, its contact 2'! interrupts thecircuit including back contact 25 of relay PBR for supplying energy of 75 code frequency to relay CTM and connects relay CTM to contact I26 of signal lever SGL so that energy of or code frequency is supplied to relay CTM depending on the position occupied by the signal lever. 11

Assuming next that the signal control lever SGL is moved to its left-hand signal clearing position, when relay HS picks up, energy of 120 code frequency is supplied to relay CTM causing energy of this code frequency to be supplied to the line Wires Y and Z, but the polarity of this energy remains unchanged, being determined by the position of the contacts of relay WLP. As the polarity of the coded energy supplied to the line wires is unaffected by movement of the signal control lever SGL, the coded energy supplied over the line wires maintains the switch SW in the position which it occupied prior to movement of the signal lever SGL.

Master code of 120 code frequency supplied over I the line wires Y and Z operates one or the other of the code following line relays NCF and RCF at this code rate, depending on the polarity of the master code.

On operation of either of the code following line relays at the 120 code rate,-assuming the switch control and switch indication relays are picked up to establish the circuit of the primary winding of the decoding transformer DT, energy is supplied from the decoding transformer through the resonant rectifier unit lZGDU to pick up the signal control relay LHR.

"On operation of -.either of the code "followin line 'relays atlthe 120 code :rate, impulses continue to be supplied ifrom the decoding transformer DT to relay IR. which continues to operate -to supply impulses of ifeed baek energy from the battery F3 to the linewires Y and Z. However, as long as relay H-KR is released, the'impulsesof feed-back energy continue to beef-normal polarity, and sinceat this time the oflice equipment is conditioned to respond only to energy of reverse polarity, the feed back ener y supplied to thelinewires is without effect. 1

When relay LHR-picks up, its contact 139 interrupts the circuit for the pick-up winding of relay TS, but relay TS is maintained picked up Icy-energy supplied over its stick: circuit.

When relay LHR. picks up, its contacts'M and 65'prevent supply of energy to relay RHDRand permit energytobe supplied to relay LI-IDR. If at this time the switch SW is inits normal position so th'atrelays N-WR and NW? are picked up, relay LHDR-is connectedto acircuit governed by traffic conditionsin the-track stretch at the left of the switch SW. "The circuitfor energizing relay LI-IDR at this time extends from terminalB at front contact I 3| ofrelay NWP; over front contact I32 of relay RAS,'back contact "66 of relay RHR, front contact I33 of relayNWR, front contact I34 of relay NWP, front eontact l sii of relay TS,'front contact I36 of'relayTR, back cont-act 1310f time element relay front contact 64 of relay LHR, the winding of relayLI-DDR, and front contact-65 of .relay LHR to terminal C.

If, when relay LHR picks up, the switch SW is in its reverse position so that relays RWP and RW'R are picked up, energy is supplied to relay LHDR over the circuit extending from terminal B at front-contact 'IIEB- ofrelay RW3F ,--over back contact I3lof relay NW-P, 'front contact [32- of relay RAS, back contact 66 of relay RHR, front contact Ml of relay RWR, front contact 1620f relay RWP, front contact [35 ofrelayTS, front contact1 3B of relay back contact 31 of relay TER, front contact64 ofrelayLI-IR; the winding of relay LHDR, and front contact 65 of relay LHR- to terminal C.

When relayLHDR picks up, its contact53 interrupts the circuit for relay LAS, which'relay releases so that'its contact ll interrupts the circuits of relay LR. When relay LR releases, its contacts Hand 46 interrupt the circuits controlled by' contact 44 of relay NWR -an'd contact 41 of relay RWR for supplyingenergy to relay WR and connect relay-WR to contact I l3 or relay NW? and to contactl'M of relay RWP So-that energy is supplied to relayWR; to cause'the' switch SW to be maintained in its last operated position.

In addition when relay LASreleasesJts contact '54 interrupts its stick circuit and establishes a'circuit overwhich energy may be supplied to theti'me element relay TER,"while contact [55 of relay LAS opens to pre ent the closin Qf-t'he circuit over which energy is, supplied to relay RHDR. a

On release of relays .LRvand LAS energy is supplied to signal relay LAI-I or LEI-I depending on the position of the switch SW. lithe switch is'inits normalposition sothat relay is picked up, energy issupplied to'relay'll-Ailsover the circuit which extends from terminalffiB at back contact -S'iLof relay LR, over hack contact 55 6f relay LAS, back-contact M of relay front'contact44B of'relay NWRand frontcoxitact M! of relay LHDR, through relay to'terminal assmta qsandprelay LAH' of signal L'A.

If the. switch stands reversed, relay LBHJis. energizediin place of relay LAHv overthe circuit'extending :from terminal. B :at contact :of relay LR- over .back contact 55-..of relayw LAS, back contact 1M9 of relay RI-lDR'front contacts 159 and ['51 of reIays RWP and LHDR, through relay LBH -toterminal'C, so that relay LBHapicks up to causesigna-l LB to indicate proceed.

It -'-will be seen that 1 the clearing of the signal LA or BB is made dependent upon the locking of the switch electrically by'the release ofreIays-LAS and LR. Relay LAS, when released, can'bepicked up again to release the switch' locking following the restoration'ofthe signal manually to stop, only after-a-time locking periodof severalminutea -as hereinafter explained. It will be seen that-sincethe circuit-for releasing relay"LAS'is controlled byrelay LI-lDR, if relay LHR is energized in an attempt-to'clear signal L'A orLB under conditions which preventrelay-LI-IDR from becoming energizedrelay-LAS is not released, and the signal 'levermay then be restored-tonorpicks up to effect the clearing maytorelease relay "LHRwithoutimposing the ,tive terminal of battery FB being connected to line wire Z. Accordingly, energy flows from wire Z over back contact i I of relay CTM, front contact ['01 of'relay 'HS, winding. I06 of relayKS from left to right, front contact 165 of relay HS, and back contact Ill of relay CTM to wire Y. The energy supplied to relay KS is now of the proper polarity to pick up'thevrelay contacts and it operates, as explained above, topick uprelays KP, KB and KSA. 7

When relay KR picksup, its contact 40 estabiisheS the circuits of th switch and signal indication lamps and energy is supplied to lamp LHK over the circuit from terminal B at front contact 40 of relay KR, eXtendingOVer front contact 82 of relay COR, front contact l2l of relay HS, and left-hand contact of signal lever SGL, through lamp LHK to terminal C. Accordingly, the lamp 'LHKis lighted'to indicate to the operator that one of the signals-governing movementof traffic fromlright to left across the-switch SW is displaying a proceed indication. In addition, at-this time one or the other of the switch indicationlamps NWK or RWK is lighted, depending-upon the-position of the switch and of its control lever WL.

It will be understood that a signal cannot be cleared unless one of the switch indication relays NWP or RWP is picked up, therebyindicating that the position of theswitch corresponds to the polarity of the'codedline currentsupplied from the office. Furthermore, the lighting of lamp NWK- or'RWK, and likewise the lighting of lamp LHK or RHK, indicates that relay COR is picked up, which in turn indicates that the switch lever WL corresponds in position to the polarity of the line current supplied by'relay' 'I shall now assume that the operaton'after having cleared signal L-A or IB as above described,

restores the lever SLG to normal to restore the signal manually to stop. The momentary opening of the lever contact I4 releases relays HS and COR, relay COR picking up again after a brief interval following the closing of contact I4 with lever SGL in its normal center position. The release of contact 2'! of relay HS changes the operation of relay CTM from the 120 to the '75 code rate so that 75 code current is supplied to the line, of a polarity corresponding to the last operated position of the switch Relay COR releases relays KF and KR and temporarily interrupts the circuits for the switch and signal indication lamps, these circuits being opened at contact 43' upon the release of relay KR. Relay HS changes the connections from line wires Y andZ to relay KS and thereby prevents its further response'to feed-back impulses of reverse polarity. At'the station, relay NCF or RCF-operates at the new code rate of '75 impulses per minute, maintaining relay NWR or RWR picked up along with relay CD but releasing the 120 code responsive relay LHR, which relay in turn releases relays LI-IDR and LAH or LBI-I, restoring the cleared signal to stop, whereupon relay HKR releases, changing the connections of battery FB to the line to again supply feed-back impulses of normal polarity. At the ofiice, relay KS responds to these impulses reenergizing relays KSA, KB and KR to light lamp NI-IK along with lamp NWK or RWK.

The apparatus at the station includes time look ing means, a will now be described, which, in the event a signal is put manually to stop in front of an approaching train, is efiective to prevent a change in route or the clearing of an opposing signal until after the lapse of atime interval sufficient to insure'that the train may either be stopped without overrunning the signal or will have entered the switch section to render the detector locking effective before the interval expires.

When the signal relay LAH or LBH releases, a circuit is completed from terminal B over back contacts 5|, 52, 53 and 54 of relays LBI-I, LAH, LHDR and LAS, front contacts I56 and I5! of relays RAS and TR through the winding of a tion to close contact I31 to prepare a circuit for i relay LI-IDR or RHDR. Relay LAS by closing contact II energizes relay LR, rendering the switch operating relay WR again responsive to' the operation of relay NWR or RWR and by closing contact I renders relay RHDR responsive to the operation of relay RI-IR to permit the clearing of the opposing signal RA orRB.

I shall now assume that the operator moves the signal lever SGL to its right-hand position instead of to the left, as in the preceding example, with the object of'clearing signal RA or RB, assuming relay LAS to have been picked up and relay TER released, as already described.

The opening of the lever contact I4 releases relay COR temporarily, thereby releasing relays KF and KR and extinguishing lamp NI-IK, but these relays pickup again when relay COR becomes reenergized, due to the continued operation of relay KS by thefeed-back impulses of normal polarity, and relay KR by closing contact I22 energizes relay HS which,.in turn, changes the connections for relay KS to stop its operation by feed-back impulses of normal polarity and to change the operation of relay CTM from the to. the 180 code-rate by completing th circuit over 'front'contact 21 of relay HS and right-hand contact I26 of lever SGL. Relays KF and KR again'release, relay'HSbeing held energized over its stick circuit including the lever, contact I8.

At' the station, relay RHR now picks up in place of re'la "LHR, and relay IR operatesat the-180 code rate to supply the feed-back impulses. ReIayRI-IR by closing its front contacts 66 and 61 energizes relay RHDR provided traific conditions as reflected by its'circuitare such'as to permit the clearing of signal RA or RB; Relay RI-IDR, by opening'contact 60, releases relay R'ASQwhich relay closes its contact 62 'in-the signal" relay circuits and opensits contact III to release relayLR and therebyclose contact to complete a circuit for relay RAH or RBH similar to those already'traced, to efiect theclearing of signal RA or RB; Relay HKR now becomes energized'overfron't contact 58 or 590i rela RBH or RAH, to supply feed-back impulses of reverse polarity "to the line to which relay KS responds, energizing'relay KR to light lamp RHK. I

Operation of equipment to provide an indication of'occupancy of the approach section This system is arranged toprovide acontinuous indication of occupancy ofthe approach sec. tion AR. without interfering with the control of the switch and signals or.v the "indications e e o .1, Assuming that the equipment has already been set into ',operation and that, signal for example; has been cleared for a train approach-,- ingfrom the rightas hereinbefore described, the line circuit beingsupplied with a master code of impulses per minute ofnormal polarity each followed by a feed-back impulse of reverse polarity, it will be seen that when'thewapproaching train enters section AT, the track rela AR releases and its contact, I00 interrupts the cir-, cuit for relay "which alsoreleases after ..a brief interval and closes its contact I01 to estab lish the circuitscontrolled by contact I 02 ofrelay IRfor energizing the half-step ,relaysTA and TB,

During the first picked-up period ,of relay IR following the release of relay AP, energy is supplied over front contact, I02 of relay IR andback contact I62 .of relay TB to the lower winding of relay TA, and relay TA picks up so that when relay'IR releases, energy is supplied overitsback contact I02 and front contact I63 of relay TA to the upper winding of relay TA and also tq'the upper winding of relay TB. Accordingly, during the first released period of, relayIR, .relay TA remainsfpicked up and, relay TB picks, up so that contact I03 of relay TB interrupts thecira cuit for supplying feed-back energyv from the battery FB to the line wires Y and Z. j

During the second picked-up period of the re-' lay IR, contact -I 02 interrupts the circuit for sup? plying energy to the, upper windings of relays TA and TB and establishes thecircuit including front contact I62 of relay TB forsupplying-e11 ergy to the lower winding of relay TB. Accordingly, relay TA releases while relay TB remains picked up. On release of relay'IR, its contact I02 interrupts the circuit of relay TB" and'it releases so that during the third picked upperiod of relay IR energy is supplied over back contact I52 ofrrelayl T BdZO relaycTA'; and isssupplietrover back. contact ,I 3: ofirelayfIB :tothef-linawiresz.

OmcOntinuedoperatiomof :relay IR, therrelays TA and'IB:"'.operate-iresuchwmanner; that: relay is picked: up: during1;,a1ternate:.: picked-up periods; of: the: reiayrIR and! is:..releaseda during the interveningepiokedmrt periods? off relayeIR; When -relay' AR ZiS'E releasedlgcontact I G-ST-of =r'e1ay TB -opera-tes:: periodically-2 atz qneehalf the code speed, whatever: this ma be, and: accordingly, theeeqnipmentroperatesso that impulses of feedback-i 'energ yaresupplied; tofithe' liner wires; dur:'- ing; alternate": ft periods: inithenmaster. code supplieditowthe lineiwiresf The-operation: of ;.the.ha1f+step-relayswTAt-and TB! is independent l off:- the polarity of the-master codaaand is also'rindependent-of th'e relay HKR and -thereforer-of the polarity; of" thevfeed =back energ so the modulation of the: feed-hack em ergyrbm relay- TB ='to--provide the approach indicaoflrelayrKS and establishes tbe.circuit.including front" contact III of relay KS'A for supplying energy? torelay.- KSA. so. relay; releases.-and relay, KSAremainslpickedrupn As. a. result Lof the. pick-up. and? release. of. relaygKagthe relays arebothlpicked up so contact 164 oiLrelyJiR establishes :tHecir'cui-t contiolledJby contact. Ifislotrelav KSAidn. supplying energy to.relays.KB andJAKR2.-, 1

Ii,',.now, duringethe second release period of relay, GEM; no ieedebackenergy. issuppliedlb'y. the field station lequipmentto. the linewires, .relay. KS remains re1eased;..rendering.. contact I 08 of-lrelayt. CTMlefiective to. interrupt! the supply OfJ GII BIE-yt), relay KSA to..-cause-it to release so-thatlenergy.is.supplled overtfront. contact I54 oft relay..KRiand, back contact. I 65' ofzrelay, KSA to.relay.KB so tfiat'relayrKBpieks up.- Diiring the. secondtpickedup peri'odof 'relay C'I'Mjienergyjismotsuppliedlto. relay KSA asits contact; H 4 is wopen-.so. that relay 1 KSA .remains released and relamK'Sial'so. remains. releasedi mime g--,- the .thirdlrellase period; of relay anrimpulse of..fedi-hacli.energy is. suppliedlover tfi'erlinewiresto.relay-KS 'and' itscontacts pick upsOJthat'contact. IIIfe-stabhshes. the circuit for the relayholding windingll ll'fand 'for. .reIaBLKSA'. Accordinglygj. relay. KS remains picked up, tlirouzlioutitlie .nextlsucceedinglelease period of relay CTM,'d1'1ring which period"'re1ay KSA: picks upsothatenergyis supplidi'over front contact I64 ofrelaylKR; fiontcontacti I65fof relaylKS A, andfiontco ntact I 6601 relay KBto' relay Contact 4 I: of'relay closes to establish the circuitj'oflampAK so-that lamp AK' becomes li'ghtdf to indicate that the approach *section is occupied. T

Diiriiig thef third' pickedup"'p'eriod of relay reItty- KSY releases-*w-liile reIay' KSA" is maintainedilpickedt up bysenergy 'sunpliecbover theiici rcuit which iricliides front'contact' I 68-- of relay; (iflMaanmfrontrcon-tact iH'd Of reiay= KSA;

chem se the :ifOHIiGhC-QI'BIEBISEEL.pBriOdaioflthfiiilfilfiyf CTM; feedeback' energy isnnotzsuppliedzoverxthe line Wires-tosrelamKSand .itremainszreleasedi and relay KSA releases so; that: energmis suppliedfito relay KB-r r ,It-lwill Joerseem-therefore-, that when reed-back energy is'supplied toithe-line wires-onlyfduring theca-lternateVofi periods in the masterrcode: thei-relay KSA. picks Alp during: thezoff" eriods irrrwhich .:feed:-.backi energy; is supplied; over. :the line w-ires and rreleases during; the+ intervening off! periods "in which feed-'backr energyyj is $1103 supplied to i the 7* liner wiress As a; result =0fr:thi-s code. following roperaticn of! rel awKwSA; ,the relays K-Br1and IAKR-"are selectively picked. up: so that lamp AKis lighted. Whenmodulated feed-.backwenergy-is supplied overrthe line 'wires relay KS picks: up onlyduriing: the: alternate. master code: off. periodsin which feed-back energy: is: suppliedtorverrthe line wires, and consequently" operates periodical-1y at areiativelyslow rate. The reIayS I ZF-and Kit are m'ade slots/enough in :releasi-ng; toinsure that relay;KR remains picked.- up widen this condition and; maintains the circuits-"for supplyingxenergy to=--relays.-KB.-v ana and to. the: switohsan'd signal/indication lamps.

If the approach. section AT: iS''I1OW"V&Cat8fl\ the s relays AR and-"AP will pick up tonintermpi; the supply; of. energy to the half -step;relays- TA and TB and contact I03: of relay TB-will remain reieasedesdthat an impulserof feed-hackenergy is: suppliedto the: linewwiresa'each timerrelaw'IR picksugw that: is,- -durin'g, each off periodrtin :the magstercode. According1y;. relay? KS :pickszrup during-.each:-ofi periodrirr the masterrcodei and contact! :I.I 0;ctrelayKSestablishes the circuiticr supplying; energy? to the winding :1 =I2- 'ofrrelay KS and .to. the winding-0t relay, sc =re1ay; remains picked :up' and-Sits contact H- l maintai-ns the circuit for supplying; Y energy to relay; 'KSA during the epicked-upv periods,- of; the :-relay r'GiIZM: Under this condition, therefore, during: the? re;- lease: pBIiOdSZOf relay Grim-energy is suppIiedFtc relay Ksfl'over'baclmcontactI38 of relay 'G DM' and front contact I I8 of? relay KS, whilesdming' the pickedr-up periods of-re1ay'G: .M': energy is supplied-to.-relay; KSA- overs back contect EH3 of. relay C'I'M-and front"contact I W- of. re'lay- KSAi As energy is supplied to'relay KSAfduringrhoth thepicked-up and the releasedmeriodt: of relay. CZIM, relayKSA is heldf steadily -pickedzrup and does-:not establish the circuit of relay: KIBrso': cone tact- ISIt-of relay interrupts-the cireuitzof terrupts thecircuit of the lamp.

A valuable characteristic OfTthG-HlOdillQtGdiOR halfr-step feed-back de'cOding; means? is" the :fact thateitwi'll not falsely'resliond; tor foreign-cur= rent supplied to the line wires; Thisienablesithis typeof: feed-ba'ckfapparatus' toibe' employed -.for safety functions for which thezusualltype ofz'feeclsback apparatus is not available:

Asex-plainedrinidetail above, relay Ks' -iss con; nected-acrossthe line Wires duringrthe releaseperiodsrof-melarC'Ih/L If-foreign currentis supe plied to the" line Wires; it WilII'piCk up 1 the? con tacts of relay-KS eachvtime the-relayFCT1Vfre= leases, and energy will'be supplied to'the'holding winding of relay KS and to: the: windingzofr re= Iay 'KSA- while during the picked-up? periods of relayfCTM- energy will.hesuppliedfimrelay over its-holding circuit. Under these-conditiens; relayKSA is constantly-pickedup andirelayslKB and AKRrema-inreleasedzd 'In'or'der for the relay KSA to follow code and energize the relays KB and AKR, the relay KS must remain released during alternate released periods of relay CTM, at which time relay K8 is connected across the line wires. Obviously, if

foreign current were supplied to the line wires,

it would not be present only during alternate re leased periods of the relay CTM, so code following operation of relay KSA cannot be caused by foreign current.

Operation of system to provide an indication of occupancy of the detector section This system is arranged so that the lamp TK at the ofiice is lighted whenever the detector section T is occupied. The circuit for lamp TK is controlled by contact 3? of relay TKR, while energy is supplied from line battery LB to winding 29 of relay TKR in series with the line circuit when relay CTM is picked up, and is supplied locally to the holding winding 8'! over back contact 85 of relay, CTM and front contact 86 of relay TKR when relay CTM is released. It follows that if relay TKR is released, it will be picked up by the first'impulse of the master code supplied to relays NCF and RCF and will be maintained picked up as long as the master code continues to be supplied to these relays.

I When the detector track section T becomes occupied, relay TR releases and its contact 33 prevents the' closing of the circuit for relays NCF and R and for the line winding of relay TKR when relay CTM picks up, and since at this time the circuit for the local winding 81 of relay TKR is open, relay TKR, releases; whereu on contact 31 completes the circuit for lamp TK and. contact 85 interrupts the circuit for windingB'l so as'to prevent the energization of this winding when relay CTM releases,

Accordingly, lamp TK becomes steadily lighted to indicate that the detector track section T is occuoied.

When section T becomes vacated. thecircuit for supplying master code to relaysNCF and RCF is reestablished by t e closing of contact 33. Consequentl'y. relay TKR in series therewith picks up and extineuishes lamp TK.

It is to he noted that the-arrangement of the apparatus is such. that relay TKR. is unaffected by operation of the half-step relays TA and TB to control the sup ly of feed-back energy to indicate occupancy of the approach section AT.

, When theapproach section AT is occupied and the detector section T is vacant, the relays TA and TB operate. as explained above, to interrupt the circuit of the feed-back battery FB during alternatepicked-up periods .of the relay IR. Howeverjthe relay IR, is picked up only during the off periods in the master code, and at these times relay TKR is maintained energized by current supplied to its holding winding. During the on periods of the master code, the relay TKR is energized in series with the line circuit, and at these times relay IR is' released and connects the linewires to relays N01 and RCF and it is immaterial whether contact. Hi3 of relay TB is open or closed.

Operation of relay TKR to initiate operation d of the system As previously pointed out, when relay PBR is picked-up, its contact 24 interrupts the circuit of the codeltransmitters and steady energyis supplied over front contact 25 of relay PBR and back contact 21 of relay. HS to relay CTM, and the contacts of relay CTM. are steadily picked up and battery LB is connected across the line'wires in series with winding 29 of relay 'I'KR'. As long as the line circuit is intact the'energy supplied through the line winding 29, of relay TKR maintains the relay picked up so that its contact 20 maintains the stick circuit of relay PBR.

When a train enters the approach section AT, relay AR releases and its contact 34 interrupts the line circuit including relay TKR and the code following line relays NCF and RCF, while contact Hill of relay AR interrupts the circuit of relay AP and after a short time interval, relay Al releases, its back contact lfil reestablishing the line circuit. Relay AP is made sufficiently slow release to cause relay TKR to release during this interval. The release of relay TKR opens contact 20 in the stick circuit for relay PBR so that relay PBR releases, remaining released after relay Al? releases to reestablish the line circult and thereby reenergize relay TKR.

When relay PBR releases, its contact 2 establishes the circuits for the code transmitters, while its contact 25 interrupts the supply of steady energy to relay CTM and establishes the circuit for supplying energy of '75 code frequency thereto so it operates to cause energy of 75 code frequency to be supplied to the line wires. The coded energy supplied to the line wires operates one or the other of the code following linerelays NCF and RCF, depending on its polarity.

Relay IR becomes periodically energized through transformer DT to cause impulses of feed-back energy to be supplied to the line wires. As relay AP is released, the half-step relays TA and TB operate as hereinbefore described to cause feed back energyto be supplied to the line wires only during alternate oif periods'in the master code. This; modulated -feed-back energy operates relays KS and KSA to pick up relays KR and AKR, to establish the circuits of the switch and signal indication lamps; and of the approach indication lamp AK,

The relay TKR also operates to initiate operation of the system if a train enters section T ata time when the system is inactive, as would occur in the case of train movement from left to right through the track layout shown. When section T becomes occupied, relay TR releases and interrupts the line circuit so that relay TKR releases to establish the circuit of lamp TK and to interrupt the stick circuit of relay PBR with the result that it releases and causes the system to function in, the manner already described.

Operation of system in response to a movement I of a traincver the switch This system is so arranged that when a train enters the detector track section the signal authorizing the train movement is put automatically to stop and cannot be cleared again unless the operator first returns the signal control lever to its normal position and the apparatus transmits energy of 75 code frequency to the field station.

For purposes of illustration, it will be assumed that the switch lever WL is in its normal position so that energy of normal polarity is supplied to the line wires to cause the switch SW to occupy its normal position, and that signal lever SGL is in its left-hand signal clearing position so that energy of code frequency is supplied to the line wires to operate the field station equipment to pick up relay LI-lIR.

W IienwrelayTLHRl iszpicked any; energmi'isi SUIT? plied'l-to;rblayflI-IDRianditzis :picli'edzuprto: cause releases of relato-"LA-si and'lto'a cause-energy? to be" suppliedito relay:LAH and thus to clearsthe signal LA;- As explained' 'above', feed'ebacklenergyssupe plied: over= the line wires operates-relay KS to pick up relaylKR' and light the switch indication lamplNwK 'and the signal in'dicationalamp As relay -I As:'.is released; the circuit ofzrelawLR is -inte1'rupted and:- it'is:released to maintain -the switch -SWin its normal position;- 7

' When a train moving to-the left ent'ers the approachsection, relays AR and 'APrelease sotli'e half st'eprelays TA" and TB operate as-explaihed above :tosupply feed-back impulses during. the alternate intervals between the-master "code inrpulses so as-to cause the *equipment at "the *cfli'ce te operate to light the approachindicationglamp AKC It has already been pointedout that when relay AR' -relea-ses the line circuit isopened at contact cutting" ofith'e supply *of master code to the relays NGF -and" R'QF for a hriefperiod terminated when relay AP releases? However, the signal control relays Ll-IRi 'and"RHR are =sufii'-' cientli 'slovr in releasing to remain-picked up=in this condition; sothati' if-a signal hasbeen olearedfit's=energizationis not interfredwitli by a-train entering the approach section Whenthe ti'a-in'enters'the detector section T; relay TRre'lasea amifbyopening its contact I 36 releases the litre relay LHDR which in turn releases the-*signalf'relay LAHtocause signal L'A-to display its stopindication and to release thesignal indication relayHKR.

The openingof-contact 33 ofrelay; 'I'-RF inter-- r-npts' tlie supply-of master code to relays-N61 aiiwRCFscY-tliat these relays" remain steadily released; releasing-relays NWR; CDand LHRI and causing relay-IR t'cremain steadily'releasedi At' the oifice; relay TKR releases to light lamp TK, as already explained, and relays KR and AKR release to'extingu'ish the switch; signal, and. approach indication lamps.

At the station. when relay TRreleases; itscontact 12 interrupts the circuit'for'the relay LR-to insure that it remainsreleasedas' long as section T-is occupied; and contact 69 of relay TRinterrupts the stick circuit 'forrelay TS so that itr'eleases with the result that its contact 68 short circuits its holding winding to render relay TS slowtc=pick up. O'n'release of relay-TS; its con'-' tact 13'aciditional1y hiterrnptsthecircuit ofsrelay LR; while contact'99 of rela-y'TS interrupts the circuit of relay IR, to preventsupply of feed bacli energy't'othe'linewires as long as relay" TS is released: '1 Y When II&YS"LAH?-: andv LHDR-c release in response to the release of the track relayTR, .enorgy is supplied toithe approachlockingstick relay .LAS. over the. circuitlwhich includes ,hack contact; of. relay LBH, baclc contactil ofl'relay LA'H,' back contact 53, of v relay, LHDR andlback contact l68of'relay'TR, and relay HAS. picks up so that its contact 54' establishes the-relays stick circuit to maintain the relay pickediupafter the detector .section is vacated andrrelay TRspick-s up.. Picking -up,.=of i the. relay. LASewhen the detectorlsectiens is occupied enables. the. operator: to

ezssvg-rce I tact J 5-? interruptsthea circuitdbrrrelawFIERIsc regain. control. of. the switch and signals as soon 7 that, energyg-is snoti suppliedri tm.rela5e-'DER; While secticn-:I=..is:occupied; V

When :therstrain: vacates.: sectiom AT; relasci-AR picliSxilpgalld establishes the circuit ofirel-awAB so that it picks up to interrupt: thevcircuitnofsthe half-steprrelayszTA and'I'Bzwhenathe train vacat'es sectionrTg-thei traeli relay; TR picks up and? itsi-contact -fiiiz'permits coded energy supplied to the line wireszto. betsup-a plied to the relays NCF and RCF, and if the signal lever SGL and the'switcli'lever' WL at"the-offi ce remain in-t'lieir left-handpositions'so that energy Of-IZQ. code frequency and normahp olarity isl-supplieolto V the linesvires, the relay NCE will operate at-this,v frequency and. energy. willabe suppliecl through the-=dccodi11g:, transfomner D311 tooagain energize. relay. LHR.

When conta-ct 33. of track relay 'IRisclosedto permit energy, to; bessuppliedover, the lineewires to relayslqCl iandRCE, theener-gysupplied from battery: LB through wind-ingdiofxrelay "DKRndur! ingsthe pickedeupperiods of.the(relay GTM picks up, the relay TKR..or-keepsit-picked upset that its contact. 85, establishes .theacircuit; for? supply ingenergy to. the. wind-high! during the released periods of relay. C'IM.. Accordingly, asasoonzas the detector section is vacated,;relay TKR-tpiclcs up and its-contact .Blinterruptsthe circuitofcthe lampflliand itcis .extinguishedltorinform-i the operator, of the l-factethat the detector. sectienphas been vacated.

The: code following operation of relay NGE causes its .contact. L1!) .to alternately establish the two circuitsifcn energizing thewinding's of--.relay PR in. series, withsthevcorresponding. portions of thee-primary. windin or the associatedtrans+ former. However, .i as, explained.=above,- the relay PR and the transformer arevproportionedrso that insufficient energy. flows through. the windings of relay PR to operate the. relay contactswhemthe code following line relays operate at code. speeds higher than the. ncoderate. Accordingly, :contact ot-relay. PB. remains in one or; the; other of its two positions .andxloes .notrectify, theeneray supplied from." the. transfer-men secondary-wind.- ing to the circuit forthepick-up-winding,oi relay TS, and relay TS will remain releasedeveniif for any reason, such as temporary interruptiomofthe linecircuit, backcontact I30 of relay LHRbee come closed;

long'as relay TS is released; its c0ntaot'135 prevents supply of energy to the line relays LHDR and RHDR and thus insures that the signals display stop indications, and contact 13 of relay TS interrupts the" circuit of the lock relay LR'to: insurewthat itremains released and prevent movementof thezswitchz. In additicn; contact:99 of: relay Ts' interruptsthe'circuit' ofi reiay IR so that-it. remains released so-that feed-back energy is not=-snppliedto the line wiresaconsee quently, the-switch; signal; andzapproach-f indie: cationzlamps at theofiice remain darkmntil'rel-ay Tsfisreenergizeda If the operatonnow wishestoeregaincontroLof the signals, he may do sobymovingthesignal lever SGL to its normal center position vwhereupon it contact IB'interrupts the sticlccircuit' for the relay HS, and it releases so that its contact 21: interrupts the: circuit for supplying energyef signal control frequencies torelay C'IM and establishes the circuit for supplying energy of '75 code: frequency to the relay CTM; Accordingly, relaysCTM causes: energy @575 code-sfrequency to, be snppliedv' to: the line wiresandithis: energys op crates relay NCF at the 75 code rate so that the energy supplied through the decoding transformer DT i no longer efiective to energize relay LHR and it releases and closes its contact I30 in the circuit of relay TS.

,. When relay NCF operates at the '75 code rate, the relay PR responds to. alternate energization of its two windings and contact 95 operates periodically and rectifies the energy supplied to the pickup winding of relay TS, causing relay TS to become. energized to establish its stick circuit including its own front contact 68 and front contact 69 of relay TR. In addition, when relay TS picks up, its contact 13 permit energy to be supplied to the switch locking relay LR over its pickup circuit and it picks up to transfer control of relay WR to the switch control relays NWR and RWR, while contact 990i. relayTS eestablishes the circuit of relay IR and it thereafteroperates to supply feed-back energy to the line wires to operate relay KS at the oifice, thereby energizing relay KR to light lamps NWK andNI-IK. The

signal to display a proceed indication requires a separate movement of the signal control lever from its normal position to the corresponding reverse position.

r The system is also arranged to prevent switch control storage, that is to say, to prevent operation of the switch in response to the movement of the i switchlever unless the switch is electrically unlocked and free to respond at the time that the lever is moved. If the switch lever is moved when the lock relay LR. is released, relay LR is held released irrespective of traffic conditions at the .switch until lever WL is restored to a position corresponding to the last operated position of the switch. I

As shown in the drawings,-switch control lever WL is in its normal position so that relayWLP causes energy of normal polarity to besuppliedto the line wires. This, energy picks up relay NCF so that relay NWR is picked up and establishes the circuit including front contacts45 and 46 of lock relay LR for supplying energy of normal polarity to relay WR and it causes the switch to cupy its normal position with the result that energy of normal polarity is supplied to relay WP and its polar contacts occupy their normal position and relay NWP is picked up while relay RWP is released.

If lock relay LR is now released because of release of one of the approach locking relays or of occupancy of the detector section, its contacts 45 and 46 will interrupt the circuit governed by the switch control; relays NWR and RWR for supplying energy of normal polarity to relay WR and connect relay WR to the circuit controlled by the switch indication relays NWP and RWP so that energy of normal polarity is supplied to relay WR to cause it to maintain the switch in its normal position.

When the approach lockingrelays LAS and RAS,and the relays TR and TS are picked up, the pick-up circuit for relay LR is established only if the polarity of the energy supplied to the line circuit is unchanged so that relay NWR is picked up. Under these conditions, a circuit is closed from terminal B at front contact of relay RAS, over front contact H of relay LAS, front contact 72 of relay TR, front contact 13 of relay TS, winding of relay LR, normal polar contact It of relay WP, and 'front contact (1 of is'bein transmitted over the line wires.

relay NWR, to terminal C,'and relay LR picks up so that its contact 14 establishes the stick circuit for the relay, while its contacts 45 and 6% transfer control of the relay WR from the indication relays NWP and RWP to the control relays NWR and RWR' to thereby permit the polarity of the energy supplied to the relay WR to be changed to efiect movement of the switch. If, while the relay LR is released, the polarity of the energy supplied to the line wires is changed from normal to-reverse, relay NWR. will be released and relay RWR will be.picked up. However, as relay LR is released, thi change in the condition of relays NWR and RWR does not affeet the energy supplied to relay WR and it continues to be energizedwith current of normal polarity supplied over back contacts 45 and 46 of relay LR so the switch remains in its normal position and causes energy of normal polarity to be supplied to relay WP and its polar contacts remain in their normal position.

If relays LAS, RAS, TS and TR are now picked up, relay LR will remain released as its pick-up circuit is interrupted by contact 1''! of relay NWR. Accordingly, relay LR remains released and maintains the supply of energy of normal polarity to the relay WR so the switch remains in its normal position.

The operator may now regain control of the switch by causing energy of normal polarity to be supplied to the line wires so that relay NWR picks up to establish the pick-up circuit of re- Restoration of equipment to its normally inactive condition This system is arranged so that the operator may cause the equipment to assume its normally inactive condition whenever conditions are such that continued operation of the system is unnecessary.

In order. to stop operation of the system, the normally open push button PB is closed to establish a pick-up circuit for relay PBR. The pickup circuit for relay PBR is controlled by contacts M and I8 of signal lever SGL so that energy may be supplied to relay PBR when and' only when the lever SGL is in its center position.

This makesit impossible to discontinue operation of the system when a signal control code This insures that the system may be rendered inactive only when the signals stand at stop, and

that the, display of a proceed 'indication'by a signal will not be interrupted if'the push button PB is depressed when a signal control code is eludes contact 20 of relay TKR. As' explained above, when the detector section .I is occupied, the relay TKR is released so its contact 20 pree merits supply of xenergy:torrelayrBBRiranfi: tlnis .makes. it impossible tto discontinue 'operati ODYbf the {system whenfthe :idetector section is ecccupied.

l The zpick-up circuit f relay-PBR'alsoiin cludes front 1 contact :2! coil:relaylflQRpwhfle:relay COR will be :released if the -rswitclfleizer 'zWL and fthe relay :WLP are .out of agreement. The relay COR, :therefore, tprevents. operation of the system bein r'discontinued .when :the switch ilever WL and :the .switchaare :out of correspondence.

llhapick-up circuit of:relay'-'PlBR also includes .backzcontact 7-2-3 :o'f relay AKR,while, as :"ex- .plained .above,rwhenithe approach section AT iszoc'cupie'd, ithemetayzAKRfismiekeda p. rAccordinglygits :contactr23 prevents supplyofi energy. to relayrBBR when the approach'sectionis:occupied andrthus'. prevents'cuttingmfhof operationzof the system at'such'ztimes'.

-.If, on closing of push:;hutton'?BB,.the .pickellp circuit. of -relay 7BBR' :is :otherwise .1 complete, :its contacts :will pickup and :contact '22 -.will establish a ":stick :circuit .toimaintain rthe arelay energized afterthetpushvtbuttonsis released. -Inzzaddition; on pickingrnp of :relay -PBR, 1' its i contact 24 interruptsxthenircuit:ofithecode transmitters, :while contact :2 Eiinterrupts theicircuitifonsupplying energy of 75rcode'zfrequencyto.relay 'CTM and establishes :the circuitfor asupplying steady energy thereto. .Accordingly, the relay .CTM. is steadily picked wup .and -;causes 'Lsteady energy to be; supplied to- ;the 1ine-.wires. :Sincerelay KS :is controlled aover back :contacts of .irelay fCT-M, it remains re1eased;andtre1ay;KR; releases-tore tinguish the switch andxsignalxindication lamps. E35

Modification shown-in Fig: 2 y

In Fig. 2 ;there is shown: a. modified 7 form .0)? .office:equipmentwhich may beemployed.implace in Figs-24s generally-similar tothat-shown iIIFig. .lA- both'inconstruction and operation but differs therefrom in that-a push-button is not :providentto render theequipment-inactive; the equipment-being arranged so that itzautomatically becomes inactive when continued --operati.on-.of the .system is not required. 7 I

The equipment of Fig. 2 further differs from that -shov vn in Fig; 1'A"in; that the relay Z-R,-wl'1icl'i replaces the relay PBR'oFthe system shown in 'Fig. 1A, is released -torender the equipment: inactivetandais picked up vto-render the equipment active. Similarly, athe :circuits .controlledvby the relay C 'JEM- are inverted :and this relay Operates when released to cause energy to be supplied from .the line battery LB-to' the line wires,-and operates when ;;picked @up ,to connect relay KS .across the line wires, while-the :other circuits governed icy-the contacts :of relay-.CTM are reversed to. correspond.

The modification shown .in- Fig. 2 further-.dif- .fers 'from-.that shown in' -Fi g. 1A :inthat :the po- .larity-. of the energy supplied torelay .CORis controllednbyr contacts of relay 1 HS -sothat-relay COR releases when relay-HS picksmp, -whiletheccircuits of the-qindication lamps are at-timescontrolled 1 by a slow pick-111p repeater relay HSP :f or the relay :HS to .thereby eliminate momentary lighting of-these: lamps on movement of Ethel-si nalcontrol-leverm I v The equipment is shown in itsenormal inactive condition. 'Atthis time,'.as:explainedinsdetail rhelow, .of the i'circuits for? energizii g-srelayazR are interrupted :and2relay':Z-R?is" released southat 'its-contactziza intermpts :theccircuit:ofcodingqer75 weavers-2 flay cl'li-Mz-andfslts icontactsrare released "with'tthe resultiimatiineibatteryiLBris eonnected- 'overzback contacts etflaa'nd 1H of codingzreiay'zc'I'lvl to the linezwires in series ewithithe lwinding fl9- 0f r elay TKR. Accordingly, relay 'IKRfistener'gized lantl itsscontact 3'i'rinterrupts the circuitxof lampflTK and itscontact ill interruptscone:circuit tor energizing relayZR.

As. relayzk isireleased, itseontact zdxinterrupts the circuitsio'f the codeitransmitters 1.5CT,:I220CT mid 1. 89 clTpxvhilezcontactln interrupts: the cstiek circuit f for relay. ZERan-d :contact 1 H2 establishes a'holdingicircuitzfor.relayICOR.

iAt :this' time; relayLCGR-iis energized by. current supplied over its 1. holding circuit 1 which extends frdm terminal :B at eontacttitaof lever SGL;:3aack Contact M0 aof'srela'fis -contacts L5 and "1610f lever wl-ycontactzft an reIay WLP; back contact 432 0f. -relayfizR lthrough :the ewinding of relay CORlin thereve'rse directionpthat is, from :right to leftpand thenee over back contact -18 I of :relay. HS -to tenninal C. Relay (COR is therefore normally energized an'd its contact" 8:2 completes'a circuit fromterminalB- over back contact weer relay HS and contactkm otre lay WLaPJforrenergizing mhe switch iin'dication lamp "fNWK, and in this :respect' the modification-shown "in FigSEZ fliff'ers from that showman Fig. 1 A. JAs reIayEC'I'M is steaJZilIyreIeaSed -the relay KS is also-steadily released so reIaySLKF andKRare released and contact" LoA Of TeIaY-KR interrupts the circuitsuof rthe 'relayslKB .and AKR with the result zthat coi'ita'et l M i-nterrupts the circuit :or lamp AK and=ccntact 23 of relay AKR- interrupts the acircuitiwliich it controls for energizing :relay ZR. In addition, as relay KR is released, its-=contact 413 Linterrupts the' pick up circuit -bf relay EQR Kbut the relay (30H is m-aintained energize'd :by currentsuppliedovei its holding --circuittraceil of that shown in Fig. 1A. The equipmentsshown 140 aboveg while cor'itactH-JJS o f relay =KR=-interru15ts *the circuits-of the sign indica'tion -lamps and-0T relay ESP, and: contact 1 2-2 of a relay interrupts the pickeup Circfiit of reIay- HS. ommovemeneer either the switch or theesignall nontrol lever the circuiv (if the relay COR -isinterrimted at-contact FBror -M. Assurning that-t he switch lever WL is operated, for example, -rlay (39R releases in -response 4:0 the lever-*operation and" its co'ntacfi 2|: estarilishes a circuit to supply =energ ylto relay ZR whicn piksmpso that-its contact tll interrupts the-holding circuit 'o'f relay G01? additiomwhen relay zRapieks up, its contact z 2" estabii'shes a 1 stick --circui t including back :contact" 1384 6? relay to maintain relay ZR Lpieked up' aslong asrelay' KR' is' released. whenrelay ZR picks up Pits conta cti l es'tablisms the circuit of 17118603841-fl1l5lfiifl36f8, while con tact -Z5 establishes the circuit for=supiilyingenergy= of "code frequency to the rlayCTM. 7

When relay COR releases, its contact ET-in'ter- -mpts the circuitsE-fnnthe' switch -indicatieri lamps, mhileaits icontact 38 lliriten upts" the pick-unciracuit'iforirelay fis. r

The :energynof 5 code f-requency supplied -to coding? relay" C'mll operatesiit to: cause energy 'of ihis code .ifrequen-cy to I be -supplied to the dine awires, .the" toir -periods in' thecode occurring the release period sl 'o'frelay C PM'and'the ii'off; periotls'Sinithe decide occurring during the ;picked-up .periods of relay' cTM, while *clurimg the picked-up periods of relay CTM, reIa'y -K S is .connected -across itheline wires and Z. 'jniiresponse to 3 thessupp'ly 16f coded energy to ;the-lineiwires the equipmentrattthe fieldstation opera-tesi as explained above, tonnove ithe :switch lithe position of the switch and the polarity of the master code supplied to the line wires are out of correspondence and, when theposition of the switch and the polarity of the master code are in correspondence, feed-back current is supplied to the line wires atthe field station during the off periods in the master code so that relay KS is periodically energized over front contacts I8 and II of relay C'IM- As a result of the code following operation of relay KS, the relays KB -and KR pick up and contact I18 of relay, KR

establishes the pick-up circuit for relay CORand, after a time interval, relay COR picks up.

When relay KR picks up, its contact I64 interrupts the stick circuit for relay ZR but relay'ZR ismaintained energized by current supplied directly over back contact 2| of relay COR.

When relay COR picksup, energy is supplied over its front contact 82, back contact I83 of relay HS, and contact II8 of relay WLP to light one or the other of the switch indication lamps NWK or RWK to indicate the position of the switch, and over front contact 82 of relay COR, front contact I16 of relay KR, and back contact I2I of relay HS to light the stop signal indication lamp NHK. 1. 7 If, atthe time relay COR picks up, the signal control lever SGL is in its normal or signal stop position as shown the pick-upcircuit of relay HS is not established and it remains released and its contact I does not establish accircuit for relay ZR. Y

Under these conditions the supply of energy to relay ZR is cut ofi when relay COR picks up. A'condenser Q is connected acrossthe terminals of the winding of relay ZR and ischarged when energy is supplied to the relay, while when this supply of energy is cutofithe energy stored in thecondenser discharges through the relay winding and keeps the relay contacts picked up fora period, such as five seconds.

Accordingly, when relay COR picks up andthe supply of energy to relay ZR is cut off; the relay ZR'is held picked up for a time-interyalby energy supplied from the condenser. Aslong asrelay ZR remains picked up, coded energyis-supplied to relay C' IM and it causes coded energy tobe supplied to the line wires, while feed-back current is supplied over the line wires and operates relay KS to supply energy to relay KR so that back contact I 54 of relay KR holdsthe stick circuit for relay ZR open and front contact, !18 of relay KR maintains the pick-up circuit of relayCOR closed. V

When relayZR releases, its contact cuts oil" the supply of coded energy to relayC'IlVL whereupon the contacts of relay CTM remain released to supply steady energy through the winding 28 of relay TKR to the line wires and to cut off the supply of energy to relay KS. Accordingly, relay KS remains released and ceases to supply energy to relay KR and, after atime interval, relay KR releases. e I

When relay ZR releases, its contact 22 inter+ rupts the relay stick circuit so that energyisnot supplied to the relay on subsequent release of relay KR, while on release of relay ZR its contact I12 establishes the holding circuit of relay COR so that relay COR remains energized after release of relay KR. relay ZR its contact 24 interrupts the circuit of the code transmitters.'. p v

When relay KR releases ,following the release of relay ZR, contact I16; of relay KR interrupts I it??? O th step si nal i dication-lamp In addition; on release of NHK, while energy continues tobe'supplied. to one of the switch indication lamps NWK orv RWK over front contact 82 of relay COR, back contact I83 of relay HS, and contact II8 of relay WLP, and the equipment is-again in its normal inactive condition, as shown.

It will be seen, therefore,*that following the movement of the, switch lever WLfrom one operative position to anothenthe apparatus'is set into operation for a time sufficient to effect the operation of the track switch and to receive a return indication of its new position and'then, if' there are no further operations .to be per-' formed, the apparatus returns automatically to its normal inactive condition. A similar sequence of operations may beeffected without'operating the track switch, that is, by pressing the switch lever to momentarily open contact I5 without rotating the lever to therebyobtain a new indication to verify theexisting position of the track switch and to also indicate that the apparatus is in an operative condition. Y

Assuming next that the apparatus stands in its inactive condition, as shown, and that it is set into operation by momentarily opening contact I4 due to the operation of the signal lever SGL from normal to reverse. In this case likewise the operations will begin with the transmission of a code as when initiated by the operation of the switch lever WL, relay KR becoming ener- I gized as above described to pick up relay COR.

If, when relay COR picks up, the. signal lever SGL stands in one of its signal clearing positions, the pick-up circuit for. relay ,HSis established and it picks up so that its contact I 24 establishes its stick circuit and its contact I15 establishes a circuit to energize relay ZR to thereby insure that relay ZR will remain picked up to cause the operation of the system to continue.

When relay I-IS picks up,- its contacts I and I81 change the connection of relay KS to the line wires so that relay KS ceases to be responsive to the impulses of feed-back current of normal polarity and remains released so that after a time interval relays KB and KR release.

In addition, when relay HS picks up, its con-, tacts I88 and I8I reverse the polarity of the energy supplied to the relay COR so that it releases again, with the result that contact 82 inter rupts the circuit for supplying energy to, relay HSP and its contact I82 does not close to establish the circuit of the signal indication lamps at this time. r

Also when relay HS picks up, its contact I83 transfers control of the switch indication lamps from the relayrCOR to the relay HSP.

After reversal of the polarityof the energy supplied to relay COR, as long as relay KR remains picked up, energy issupplied to relay COR over its pick-up circuit which includes front: contact I19 of relay KR. Because of the slow pick-up characteristic of relay COR, its contacts remain released for a period subsequent to the energization of relay HS and thus prevent the energization of relay HSP. Q

It may be that relay COR will pick up shortly before the release of relay KR under this condition, in which case, a circuit is closed from terminal B at contact 82 of relay COR, over contact I16 of relay KR and front contact I2I of relay HS through relay HSP to terminal C, but relay HSP does not operate because of its slow pick-up characteristics. As soon as relay KR releases-the circuit for relay HSP is openedat contact I16, consequently contact I82 in the circuitforlamps are LHEnndRH-Kaemainsmpen. :Furtherrhora'i'the connection from terminalB atiicontact 8210f relay GOR Tto zthesicir'cuit forrlampsNWK andiRWK-Iis open atilback contact 11-83 :otrlayflS, consequently, all :of the switch rand isignal indication lamps are dark at this time. i 1

When: relay picks. up, its front .contact zl connects :coding relayr CTM .to contact I 25 of :lever SGL so .that energy of 120 or 180 code frequency isssuppliedlto relayJCTM; which relay nowoperatesito supply'energy. of-the same code frequency toithe -iline circuit 'withttheresult that the equipment at the field station causes the selected signal to -display a proceed Eindication as a result :o'i whichrifeed-back energy f reverse polarity is suppliedtmthe' lineiwires. This feed back current ofrzreverse polarity operates" relay .KS 'i to pick up relayiKR or.atofholdliitgpickedup: if it has not released; contact. H 8 of 2 relay completing the circuit;- ior: relay COR;: which :relay picks up) and inxturn ibyiclosing iits front contact 82energizes relay HSP. After a brief period-therefore, contact 51:82 70f :relayzI-ISP 'closes to completea c'ircuit over front :tcontazct :183 :of relayefis to light the switch flndicatibniilamp Ki or TRWKJ and-Uver the :si'gnal clever contact 1! I to ilightWhe signal mdica't'iondamplLHKtor Y f;

itnwill Ibe seen ,-'that :the lamp circuits fare so arranged that when relayFI-IS pifcksup'; the switch indication :lamps are iplaced under'fthe control of ar'layzI-ISP and, since :this relay iisslow topi'ck up; :therflashing .of one of-itheseiilamps does not occnrzwhenirelay. CoRipi'cks'uplto :energizei relay HSeanditherby release relay KR; l

tWh'en 2a trainenters lthe 'switch: e'ctioniT -to releasecrelay 'IR and Jthereby cut oiffi he-supply ofrfeede'back :energy. from therline wires, :srelay remainsrrelea'sed, releasing relays KF and KR When relayi'KR, releases, "'it opensu'contact 418 iii. the pickup circuit for relay COR- andmontact 1:16 in thecircuit for relaysI-ISP.

1 .Accordingly, irelay HsP releases; its contact 51 8 2 interrupting 1 the ::-switch andisignai iindicaticn 1amp::circuits, land attthisfltirne 'as explained in connection withlFig, 1 A,:relay mKR releasesno light the track:iindieationllampF'EK. 1

: llvhen relayi-KR'releases; it also closes its mack contact-164 to completeith'e'stick circuit-donrela'y ZRrwhich'isfthereby' heldlienergized tormaintain thet'coding systemrinioperation. I 1 31f :lever SGL is nowzreturnedfito' its normal tenteriposition, its iconta'ct :I=8 f interrupts the: stick circuit for relay HS, which relay releasestd shiit the circuitxfor relay C'I'M to thez 'cont-act oi -the code-transmitter 150T. I

When the itrain' vacates se'ctioni T, i relay TR piclcs'up, "closing contact to cause mastere code impulsesi'rto the supplied through' relay TKReto relays: NCF ahd RCF, sot-that relay picks up "to extinguish lamp TK. Assuming -ltheseto be of inormalpolaritvtrelay NCFrresponds; energizing relays NWRtandCDaand causing'rel ay PR t '.:operate :at the "same rate to' pick up relay TS, as :already explained. When relay T S picks:np, its contact 99 completes the circuit ier relay lR which therefore oprates' to supply' fieed '-back impulses of normalpolaritytrtothegline circuit over :the 'back contacts of' relay- HKR- .iAccordingly, relay KS operates to pick up relays KF, KRu-and KSA. RelayKR closes-contact "M8 to complete thezpiok-up circuitior r'elaYECOR and, thensafter a brief period-relay GR; picks up-to complete circuits at contact 82 over back contact 1.83 of frelay "HS r and contact l F8- 6f a WL'P tozenergizei ona of the switch! indication z lamps cantata NWK QI' EWK, and overicontact 15 of relay;KR, and hack contact 121 sof relay -:HS= to.the.: stop 'signaliindication.lampNHK. I

When r'elay-GOR; picks up, itsscontact "2 liinterrupts one circuit rior energizing relay 'ZRland, at this sti'me, contact '2 0 J of :relay TKR 33.150 pic'ked npgwhile if :relay AKR' is released, indicating that theapproach section is unoccupied, as assumed, all the circuits "for "energizing relay ZR arenow openandyafter a'time'interval, relay ZR releases and cuts offithe supply of energy to relay -C'IZM. Relay CTM then remains released to cause steady energyto besupplied to 'theiline wires and relay Ks remains lreleased. Accordingly,' relay:KR. releases-and its contact I16 interrupts-the circui-t'of thestop signal indication lamp NHKandcontact H8 interruptsthe pick-up cir cuit 10f relayJjCOR, but Irelay COR is maintained energized by current suppliedover it holding circuit incl-uding back 'contact H2- of relay ZR,the

V willbe prevented-from following the movement of the switch leveriand the result will be'to clear'the signal 'for the existingroute. l-loweve'r if the switch lever is operated, and if immediately thereafter the signal lever is operated,- the "movement of l the switchlever prior to movement: of the-signal lever causes movement of the contacts ofrelay'WLP to change the polarity of themaster code supplied to the line'wires and thus-cause movement of the switch. ---Movement of the switch lever also causes release ofthe relay COR so that on movement of the signallever, the pick up circuit for relay HS is not established. Accordingly, movement of the signal lever following 'movement' of theswitch lever is not-immediately efiective to pick up relay new cause signal control codes to be transmitted. However, this movement of the signal lever is stored", that is, becomes effective-as soon as an indication is received comprising feed-back impulses of nor malpolarity, therebyindicatin that the'switch has responded to the switch lever operation. When'this occurs relayKR picks up and itscontactl-ZZcompl'etes the circuit-for relay HS which then picks up to initiatethe control code for clearing the signal-corresponding to-theposition of'lever' SGL, and the system continue in operationas long as the-signal remains at clear, and in addition,- until the signal is restored to stop, sec tions T and ATare vacated and a signal stop indication is received, indicating that lever 'SGL has been restored to its stop position"topick up relay'TS.

It willbeseen that since energy issuppliedto relay 'ZR'over back contact 20'of relay TKR, 'ifa train enters either the approachsectionor the detector section when-the system is in its inactive state, relay ZR will pick upto set the coding system intooperation. V

When relay ZR piclss up,-even'though' thei releasewfrelay TKRis but momentarmasis the case,- for example, hit is due to the operation of relay and AP "whens train enters the approach'section, relay ZR completes its stick circuit at contact 22- over back contact I64 of relay KR, and so will be maintained energized to keep the coding system in operation until the proper conditions are obtained to permit it to again assume the inactive condition. For example, if the system is set into operation by a train entering the approach section, relay AKR becomes energized to supply energy to relay ZR over contact 23, so that the coding will not be discontinued as longas the approach section remains occupied. As explained in connection with Figs. 1A and 13, when the approach section is occupied, feedback current is supplied to the line wires only during alternate off periods in the master code and this feed-back energy causes relayKSA to operate so that relay AKR. is picked up to light lamp AK.

The condenser Q delays release of relay ZR long enough to insure that when a train enter the approach section and initiates operation of the system the relay ZR will remain picked up and maintain operation of the system for a period sufficient to enable relay AKR to become picked up and establish a circuit for relay ZR and thus insure continued operation of the system.

It will be seen, therefore, that the modification shown in Fig. 2 is arranged so that it automatically operates to discontinue operation of the apparatus when conditions are such that further operation of the system is unnecessary. Before operation of the system is discontinued, the signal lever SGL must be in its signal stop position to indicate that a signal control code is not being transmitted, and the switch lever WL and the relay WLP must be in correspondence so that the polarity of the energy supplied to the line wires agrees with the position of the switch lever. In addition, feed-back current of normal polarity must be received over the line wires to indicate that the signals are at stop and that the position of the switch corresponds to the polarity of the energy supplied to the line wires, while relay AKR must be released to indicate that the approach section is unoccupied and relay TKR must be picked up to indicate that the detector section is unoccupied.

If all of the conditions mentioned above are met, further operation of the system is not required and its operation is automatically discontinued, while operation of the equipment is automatically initiated on a change in any one of these conditions.

Although we have herein shown and described only one form of remote control system embodying our invention, together with a modification which we may employ, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention. 7

Having thus described our invention, what we claim is:

1. In a remote control system, in combination, an cfiice and a station connected by line wires, a track switch at the station, a signal for governing trailc movements over the switch, means at the cfiice for supplying to said line wires master code consisting of current impulses separated by off intervals, means at the office for causing said master code current impulses to be of one relative polarity or another and for at times causing said current impulses to occur at a first selected rate and at other times to occur at a second selected rate, switch and signal control means at the station governed by master code current supplied over' said line wires, said means being selectively re-' sponsive to the relative polarity of said current for operating the track switch to its normal or its reverse position, said means being effective to" clear said signal when. and only when said current impulses occur at said second rate, means at'the. station governed by said switch for supplying im-i pulses of feed-back current of one relative polarity to said line wires during the off periods in said master code, means at the station governed by said signal for supplying impulses of feedback current of the other relative polarity to said line wires during the off periods in said master code, a code following detector relay at the office operated by feed-back current supplied over said line wires, said detector relay having a contact which is moved from a first to a second position when and only when current flows through the relay winding in a given direction, means effective according as the master code impulses supsaid detector relay.

2. In a remote control system, in combination,

an oflice and a station connected by line wires, a track switch at the station, a signal for governing traific movements over the switch, means at the office for supplying to said line wires master code consisting of current impulses separated by oiT intervals, means at the office for causing said master code current impulses to beef one relative polarity or another and for at times caus-I ing said current impulses to occur at a first se.-'

lected rateand at other times to occur at a second selected rate, switch and signal control means at the station governed ,bymaste'r code current supplied over said linewires, said means being se lectively responsive to the relative polarity of said current for operating the track switch to its normal or its reverse position, said means being effective to clear'said signal when and only when said 1 current impulses occur at said second rate, means at the station governed by said switch for supplying impulses of feed-back current of one relative polarity to said line wires during the off periods in said master code, means at the station governed by said switch and by said signal for sup-' plying impulses of feed-back current of the other relative polarity to said line wires during the off periods in said master code, a. code following detector relay at the ofiice operated by feed-back current supplied over said line wires, said detector relay having a contact which is moved from a first to a second position when and only when current flows through the relay winding in acurrent flows through the relay winding in said" given direction when the feed-back current is of said one or said other relative polarity, switch indication means responsive to operation of said 1 detector relay by feed-back current of eitherrela-' tive polarity, and signal indication means re-.' sponsive to operation of said detector relay by feed-back current of said other relative polarity only.

3. In a remote control system, in combination,

,an ofiice and a station connected by line wires, 

